Effects of laser shock peening on mechanical behaviors and microstructural evolution of brass

The mechanical behaviors and the microstructures of brass induced by laser shock peening (LSP) are investigated systematically. The compressive residual stresses (CRS) and the micro-hardness in surface layers are performed using X-ray residual stress tester and hardness tester respectively. The microstructures of the deformation layers are characterized using transmission electron microscopy (TEM). It is found that the CRS and the micro-hardness increasing are accompanied by improving laser pulse energy. The deformation layer induced by 4.5J LSP is divided into top surface layer, SPD layer and MPD layer according to the microstructures and CRS. The equiaxed grain size in the top surface layer after 4.5J LSP impacts is approximately 20 nm to 30 nm. The grain refinement process during LSP impacts can be described as follows: (i) dislocation structures are generated by strain and strain rate induced laser shock wave; (ii) original coarse grains subdivide into sub-grains with dislocation tangles (DTs) and dense dislocation walls (DDWs) forming at their grain boundaries; (iii) dynamic recrystallization (DRX) in sub-grain boundaries takes place due to the dislocation array transitions; (iv) new grain boundaries are formed in sub-grains, then they are subdivided into nano-scale equiaxed grains with the accumulation of plastic deformation.